I'm not sure, tbh, though I suspect it's due somewhat to the general technical incompetence of (terrorist & gang) organizations. Bright people aren't exactly attracted to the idea of joining an organization which doesn't value life highly, and the bright ones that do enlist may be likely to be conscripted to work on other projects or killed by enemies/rivals. It's doable by hobbyists, but doing it with the scale/accuracy needed to be dangerous is a complicated endeavour that doesn't lend itself well to this kind of organization.

Fly a drone carrying a 500gram camera behind a tall building. You’ll learn the 6 things that stops this whole idea working. It’s consigned to the movie plots for the foreseeable future.